The present invention relates to a conveying mechanism for conveying an object to be conveyed by rotation of a conveying roller.
Generally, a conveying mechanism for conveying a sheet of paper or the like is mounted on a printer, a copying machine, and the like. In the conveying mechanism, an encoder for controlling rotating operation of a conveying roller for paper feed is provided to control a paper feed position. For example, there is an encoder constructed as follows. A disc in which a plurality of slits are formed is attached to an end of the conveying roller and transmission light leaked from the slits when the disc is irradiated with light is detected by an optical sensor or the like, thereby obtaining the rotation amount of the conveying roller. Further, another encoder is also disclosed in which a magnetic disk having a magnetic pole pattern on its surface and a magnetic drum are rotated synchronously with a conveying roller to generate a magnetic signal corresponding to the magnetic pattern and, by detecting the magnetic signal by a magneto-resistive effect (MR) element, the rotation amount of the conveying roller is obtained (refer to, for example, Japanese Patent Laid-open Nos. 2001-74499 and 2002-206950).
In recent years, the improvement of precision in controlling the paper feed position is being demanded. The improvement of precision in controlling the paper feed position is achieved by, for example, improving detection precision by increasing the size of a medium such as a disc or a magnetic drum and accurately adjusting the rotation center axis of a conveying roller so that stabler rotating operation is performed.
Recently, as a printer, a copying machine, and the like are being miniaturized, miniaturization of the encoder is in increasing demand. However, as the miniaturization progresses, the influence on the error in a conveyance amount of a paper sheet caused by a play between the conveying roller and the bearing increases. This happens because the conveyance amount is detected based on only the rotation amount of the conveying roller and the error amount of slight movement of the conveying roller based on the play is not considered. Therefore, it is sufficient to reduce the play by assembling the entire conveying mechanism with extremely high precision by using, for example, a bearing having high-precision dimensions. However, it makes the mechanism itself complicated and increases the number of parts. Consequently, it becomes disadvantageous from the cost viewpoint.